


Human Lie Detector

by torchwood221b



Category: Sherlock (TV)
Genre: Gen, M/M
Language: English
Status: Completed
Published: 2015-02-04
Updated: 2015-02-04
Packaged: 2018-03-10 10:34:38
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,644
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/3287114
Author URL: https://archiveofourown.org/users/torchwood221b/pseuds/torchwood221b
Summary: <blockquote class="userstuff">
              <p>John has synesthesia. Sherlock has to experiment with it.</p>
            </blockquote>





	Human Lie Detector

**Author's Note:**

  * For [MyLittleCornerOfSherlock](https://archiveofourown.org/users/MyLittleCornerOfSherlock/gifts).



> For mylittlecornerofsherlock's prompt request of "John has synesthesia."

"He’s lying," John said to Sherlock as they watched Lestrade interrogate a suspect from behind the two way mirror.

"Of course he’s lying," Sherlock told him, "its obvious, he keeps looking down and to the left. If he were telling the truth he’d be looking up and to the right, well unless he’s… Wait how did you know he was lying?”

"His words changed color," John admitted. The army doctor had lived with his synesthesia condition all his life and to him it was perfectly normal to see the words people spoke turn some kind of color.

"I don’t understand," Sherlock replied.

"I have synesthesia," John explained to his flat mate, "you can look up the specifics but as it pertains to me when people speak I see their words in color. When they lie the words turn red."

John watched as Sherlock processed this new information, he could almost see Sherlock filing it away in his mind palace under “further study.”

"How accurate are you?" Sherlock asked intrigued.

"I don’t know. I’ve never tested it, not really, I just confirm my suspicions every so often. It’s fairly easy to do when you’ve got blood work and test results to look at," John shrugged.

"Want to test it now?" Sherlock offered hoping John’s answer would be yes.

"If I say no you’ll just find a way to test it anyway," John chuckled.

"Is that a yes?" Sherlock questioned pleased.

"Yes Sherlock, we can test it," John agreed.

It took three days for Sherlock to work out just how he wanted to test John’s abilities as a human lie detector. The first set of tests would occur at the yard, Sherlock had selected a handful of cases and intended to show John the video taped interviews of the suspects involved. As an additional challenge he also acquired transcripts of older interviews to see if John could also detect lies in the written word.

The second test would involve live testimony either in court or again at the yard if there were cases which warranted their interest and the third and final test would pit John’s abilities against the best liar Sherlock knew - Mycroft.

—-

The First Test

"So how is this going to work?" John asked.

"It’s going to be a matter of trial and error, these first few won’t count and they’re short enough that we can see how best to proceed. Why don’t we try discussing the first one once it’s finished and see how that goes. Your memory isn’t terrible," Sherlock instructed before pressing play.

"Well?" Sherlock asked when the interview was over.

"It depends on how you’re counting, there were two out and out lies and a half truth," John began, "he lied about when he got home and who he was with but not where he was, well not completely anyway. So how did I do?"

"You got everything right," Sherlock told him, "even the part about where he was. His mistress lives above the pub he said he was at and he made a point to stop in for a drink before going up to see her. I take it you see half truths differently."

"Yes, usually I see the words turn orange, sometimes grey, it depends on the context," John explained.

They spent the better part of the morning looking at interviews for a variety of different offenses. John was most accurate when it came to men, teenagers of both sexes, kids and the elderly. The army doctor faired less well detecting the lies of women, not that Sherlock was the least bit surprised. John’s synesthesia interpreted 5 - 10% of the women’s out and out lies as half truths. Based on Sherlock’s calculations John’s synesthesia was just as accurate as a lie detector test and while Sherlock would never be the type to blindly trust the results of a polygraph he was willing to admit that John’s abilities did have their benefits.

—-

Homework

"Here," Sherlock said presenting John a stack of transcripts when they got back to the flat, "consider this your homework. Highlight the lies and when you’re done I’ll correct your work."

"It doesn’t work like that," John told him, "I can’t see the lies when I’m reading words on a page."

"No?" Sherlock clarified, "well try anyway, consider it an exercise in detective work if you must."

John rolled his eyes and took the transcripts.

"You can skip the third one," Sherlock told him, "and the fourth. They’re rather dry and don’t contain enough untruths to merit reading now that I know your condition doesn’t extend to the written word. In fact start with the fifth one, divorce case, I’d like to hear your take on the judge’s ruling."

"Sure," John replied not even bothering to argue.

He finished up the divorce case and flung it across the room so Sherlock could grade it.

"Hey! What did I ever do to deserve this?" Sherlock said as the transcript hit him square in the chest.

"You may sound annoyed with me but you aren’t," John chuckled and opened the next transcript of his homework assignment.

"Let me guess my words turn yellow when I’m pleased," Sherlock said sarcastically.

"Actually they sparkle like a glittery rainbow," John replied straight faced.

"Seriously?" Sherlock asked shocked.

"No."  
—-

The Second Test

The second test as initially conceived was scrapped due to the fact that Sherlock found every case at court boring. Instead, Sherlock decided to see how John faired against the second best liar he knew - himself. To this end he decided to slip random incorrect facts and deductions into their conversations throughout the rest of the day.

"Is this the new test?" John asked when Sherlock started making deductions about random pedestrians during the cab ride back to 221b.

"I don’t know what you’re talking about," Sherlock replied.

"You’re lying, just like you were lying about the girl in the leather pants being a tattoo artist, and the guy in the purple jumper being a coxswain," John told him.

"You missed one," Sherlock chided him.

"No I didn’t," John protested.

"Yes you did," Sherlock insisted.

"If you’re talking about Mrs. Hudson’s having a tattoo, she does," John replied.

"Is it a butterfly?" Sherlock asked when John didn’t supply any further information about their land lady’s ink.

"No," John replied.

Sherlock spent the rest of the cab ride trying to guess just where Mrs. Hudson’s tattoo was located and what it was. He was still guessing when they walked to Angelo’s to have lunch.

"Oh I give up," Sherlock declared when they sat down.

By the time they were done with lunch Sherlock had also given up on the second test. He and John had lived together long enough that before Sherlock even finished his sentence John instinctively knew that he was about to lie. It probably didn’t help that the consulting detective didn’t know many random facts to fudge in the first place.

"So what’s the third test?" John asked on the walk home.

"I’m going to pit your skills at lie detection against the best liar I know, Mycroft," Sherlock told him with a smug smile.

"That’s fine with me but Mycroft isn’t the best liar you know," John teased.

"I am not inviting Moriarty to the flat just to test you!”

—-

The Final Test

For the final test Sherlock gave Mycroft permission to divulge certain information about his childhood to see if John could read his brother as well as he’d read criminals and suspects. Mycroft arrived just after breakfast with some excuse about why he’d been late.

"Have we started already?" John asked Sherlock while the elder Holmes removed his coat.

"Apparently," Sherlock smiled, "tea brother?"

"Please," Mycroft replied and took a seat.

"Are you going to tell me what actually made you late?" John asked.

"I’m afraid you don’t have the proper clearance," Mycroft told him.

"Not the whole truth but better," John smirked.

"He is good," Mycroft remarked as Sherlock handed him his tea.

"I told you," Sherlock said fighting the urge to stick his tongue out.

"Sherlock May have deleted the solar system but his favorite movie as a child was Star Trek: The Motion Picture, he still watches it at least twice a year," Mycroft began.

"I do not!" Sherlock shouted crossing his arms in annoyance, "stick to the pre-approved topics of discussion!"

John was tempted to call both of them out on their lies but then Mycroft divulged another fact about his brother’s childhood.

"He has his stuffed bee from when he was little hidden in the back of his closet," Mycroft continued, "he slept with it until he was ten."

"Mummy made Mycroft take ballet lessons because she thought they would make him less clumsy," Sherlock retorted.

"Sherlock took them too!" Mycroft declared.

"The only way Mycroft ever got dessert as a teenager was to sneak it because he never ate his vegetables," Sherlock shouted.

"He single handedly ruined Christmas on three separate occasions," Mycroft shouted back.

John was laughing so hard that he was crying, he knew the second Mycroft opened his mouth that he was in for an interesting morning. While his instincts told him that it was highly unlikely that either Holmes was lying he wasn’t relying on his synesthesia like he was supposed to be. The Holmes brothers revealed another half dozen secrets before they realized that John was so far gone that he wasn’t even listening anymore.

When the army doctor finally regained his composure Mycroft had left.

"Sorry I ruined your test," John apologized.

"I’d say we could try again but I think you’ve learned enough about Mycroft and me for the time being," Sherlock admitted.

"Whatever you say," John agreed, "just one question though, when Mycroft said you were in love with me was he lying?"

"Yes," Sherlock said quickly.

His words turned red.


End file.
